Vaccination and the immune system

Videographic explaining how vaccines work. United States hailed progress in turning around its troubled Covid-19 vaccine rollout, as the European Union said it was on track to meet jab targets and Asia's inoculation drive gained pace on Friday. VIDEOGRAPHIC

Video Transcript

- When a pathogen, a virus, or a bacterium, is introduced into the body, it multiplies and attacks cells. This is known as an infection. Recognizing this microbe as a foreign body, the immune system deploys two defense strategies using various types of white blood cells. First of all is the innate immune response. Macrophage are at the heart of this.

These killer cells swallow up intruders, whatever they are, to destroy them. Phagocytes capture and eliminate toxins. This rapid and localized reaction can stop or slow down the infection. But that's not always enough. And that's where lymphocytes come in. They're defender cells which can identify the invader thanks to its characteristic molecule-- the antigen. Each lymphocyte is adapted to attack a particular virus or bacteria. As soon as it identifies the antigen, the lymphocyte multiplies.

B lymphocytes have the capacity to produce vast numbers of antibodies. Circulating around the body, antibodies latch onto these antigens and neutralize them, allowing macrophage to eliminate them. T lymphocytes identify and destroy infected cells. The problem is that on first contact with an antigen, the immune reaction is slow, taking several days, giving germs time to unleash an illness. Fortunately, the body remembers its enemies.

Following an infection, antibodies and lymphocytes are left with a memory. They therefore react if the same pathogen reappears. The immune reaction is much faster and the body eliminates the attacker before the illness develops. Vaccines work by exploiting the immune system's memory. Vaccination simulates an infection, training the immune system, and enabling it to develop weapons to fight back. This is done by introducing a germ which is dead or inactive or just a fragment of the germ into the body.

The vaccine triggers an immune reaction without causing the illness. The organism produces lymphocytes, which memorize the invader and antibodies in preparation for any future attack. The power of these antibodies and lymphocytes tends to diminish over time, which means top up vaccinations are sometimes necessary.